13. Total Power (Mark IV)
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13. Total Power (Mark IV) |
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13.1 Single Source
The Total Power observations are conducted with the Mark IV and the Field System, through the ONOFF procedure.
A) CREATE YOUR OWN OUTPUT FILE
It is necessary to create your own output files before starting the procedure :
log=<filename>
The file will be located in the directory /usr2/log
B) SET THE OBSERVATION PARAMETERS
onoff=rep,int,cutoff,beam,timeout,devs
Where :
| rep | Number of desired on-off cycles (default : 2) |
| int | Integration time (seconds) per each point (default : 1) |
| cutoff | Elevation (degrees) over which the on-off cycles are executed in elevation and not in azimuth (default : 75) |
| beam | Number of beams between the ON and OFF position (default : 3) |
| timeout | Waiting time (seconds) to reach the source, over which the procedure stops the acquiring (default : 120) |
| devs | Label of the acquisition system :allvc (all the videoconverter), all (all the videoconverters + all theIF distributors), v1...vf (hexadecimal list of the desired videoconverters), i1...13 (list of the desired IF distributors) |
To view the summary of the set parameters :
onoff=?
C) START THE OBSERVATION
To start the observation type the command :
onoff
A list of summarizing informations is shown, in the following figure we show an example related to an observation with the SX receiver :
Fig. 13.1 : Summary shown at the beginning of the observation
The listed parameters are :
- De : videoconverter label
- Center : central frequency of each device
- Tcal : calibration noise temperature
- Flux : flux in Jansky, if the source is a calibrator, 1 (default value) otherwise
- DPFU : maximum of the gain curve
- Gain : scale factor to obtain the gain at the elevation of the observation
- Product : gain at the observed elevation
- LO : local oscillator frequency
- T : source type (p=point, x=extended)
- FWHM : antenna beamwidth
D) OUTPUT DATA FORMAT
The following figure shows an output example :
Fig. 13.2 : Output shown at the end of the On-Off cycles
The listed parameters are :
- Source : source name
- Az/El : source coordinates
- De : device label
- I : number of IF distributors
- P : polarization
- Center : central frequency of each device
- Comp : receiver linearity (ideally equal to 1)
- Tsys : system temperature
- SEFD : System Equivalent Flux Density (Tsys/Gain), negative values point out unreliable measures
- Tcal (j) : ideal temperature (Jansky) of the noise calibrator computed by the Field System
- Tcal (r) : ratio of ideal and real noise calibrator temperature (should be 1 or close to 1)
